Acute respiratory tract infections are the major cause of pediatric hospitalizations and deaths worldwide (Bryce, Boschi-Pinto et al. 2005). During the cold months, respiratory tract infections caused by viruses are exacerbated and produce an increased number of cases, a situation that acquires the features of an outbreak. The viruses causing these epidemics in the pediatric population are mainly respiratory syncytial virus (RSV), adenovirus (ADV) and influenza virus. Another causative agent of respiratory tract infections is metapneumovirus (hMPV), a recently identified virus and which causes severe respiratory infections in children under two years of age (van den Hoogen, Herfst et al. 2004), although its diagnosis is not widespread. However, RSV is the major causative agent of acute respiratory tract infections in infants worldwide, causing severe outbreaks in winter months. According to WHO, the virus infects 64 million people annually, of which 160,000 die (www.who.int). Infection by this virus causes a wide range of clinical conditions, which may be mild such as rhinitis or more severe, such as pneumonias or bronchiolitis; the most severe diseases are seen in infants, preterm, children with congenital heart diseases and in immunocompromised children (Cabalka 2004). In addition, the infection caused by this virus is extremely common and recurrent, since almost 100% of children over three years have presented at least one episode of RSV infection (Bont, Versteegh et al. 2002). Since this infection does not leave adequate immunological memory reinfections are frequent, declining its severity with increasing patient age. However, reinfected individuals act as reservoirs and are a source of infection for infants younger than 1 year of age, those who develop severe respiratory symptoms. In Chile, during the cold months (May-August) this virus is the cause of 70% of acute lower respiratory tract infections requiring hospitalization (Avendano, Palomino et al. 2003), being the cause of the death of 0.1% of them. Although this percentage is low, the large number of cases makes the number of deaths very significant. This situation causes the saturation of emergency healthcare services, which often has made necessary the implementation of emergency measures in health services, including the conversion of hospital beds for pediatric patients, suspension of elective and scheduled surgeries and recruitment of supporting staff during the months when the outbreak occurs. The RSV diagnostic method often used in hospital facilities is a diagnostic test based on the detection of viral antigens by direct immunofluorescence of nasopharyngeal swabs. The limitation of this test is related to the need of having trained personnel for processing and analysis of samples and, besides, the results of said test are not immediately acquire, leaving a period of time within which the patient remains undiagnosed, but the infection continues its course. Due to this problem, the development of efficient monoclonal antibodies, which can be used for creating alternative detection test for RSV requiring minimum training and being fast to perform (as, e.g., immunochromatographic test), appear as necessary alternative to meet this need, since they allow the specific recognition of viral antigens in samples from patients infected with RSV, and also requiring a small amount of sample. Thus, our invention results in an antibody capable to detect low amounts of RSV antigens very efficiently and effectively, allowing the development of a fast, efficient and accurate alternative detection and diagnostic method for patients infected with RSV, in order to establish an appropriate and early treatment having effect in the development of the disease. Furthermore, the efficiency of our antibody allows us to suggest their use for the preparation of pharmaceutical compositions for treatment and/or prophylaxis of RSV infection. The antibody of the invention is specifically a monoclonal antibody recognizing M2-1 protein of human RSV and which is secreted by 8A4/G9 hybridoma.